Optical devices including display devices such as a liquid crystal display device, OLED, etc. are subject to acid or alkaline chemical treatment during their manufacturing process and when wiring electrode layers are prepared, they undergo harsh treatment procedures, for example, a surface is exposed to localized high temperature heating by sputtering. Thus, in order to prevent the devices from being damaged by such treatment, a protective film having resistance is installed on the surface during a series of treatment procedures.
As the protective films have to withstand harsh treatment procedures during the processing, they are required to have excellent adhesive property to a substrates or a lower layer of the protective films, and excellent chemical resistance, light transmittance, insulating property, UV resistance, heat resistance and water resistance. Further, they have to avoid deterioration such as coloring, yellowing and whitening over long period of time, and in a case that the protective films are applied to color filters of color liquid crystal display devices, it would be even better if they can flatten the differences of the color filters.
Thermosetting resin compositions containing a polymer having a glycidyl group have been previously known as a material for forming the protective films having such several performances but because of their weak chemical resistance and heat resistance, they can easily cause cracks including deformation due to contraction and expansion of the protective films when treated with chemicals or locally exposed to high temperatures. The thermosetting resin compositions having a glycidyl group are generally formed into protective films at temperatures higher than 220° C. This process causes a problem if a substrate vulnerable to heat is used, as in organic TFT processing, flexible displays, and OLED processing. In other words, as substrates to be used for flexible display processing cannot withstand high temperatures, protective film-forming conditions should be low temperatures; organic light-emitting devices in the OLED processing are likely to be degraded at high temperatures; and materials used for the organic TFT processing also show vulnerable properties at high temperatures so that the thermosetting resin compositions having a glycidyl group have a difficulty to apply. Accordingly, there is a need of developing a material capable of easily forming a protective film at a low temperature and having improved physical properties such as chemical resistance.